How to Protect Wood in the built environment
Seasoning the Wood: Early Treatments Used to Prevent Rot
Wood is certainly not a new building material, with structures built from wood dating back many centuries. Though today’s focus in preservation is almost entirely on paints and stains, it’s worth noting that early structures had no such exterior finish. Those structures are still standing today thanks to something known as “seasoning” the wood. Many of the earliest wooden structures were built with wood that was allowed to fully dry out, removing a significant portion of the water content from the wood. After drying, the low moisture content allowed wood to deflect, rather than to absorb, rainwater and other sources of moisture. This strengthening of the beams essentially served as an early form of weatherization, and it’s still effective for those structures today in many cases.
Another early practice designed to reduce the potential for rotting beams came along some time later and today that process is known as lime washing. This process involves mixing lime and tallow together with water and then spreading that compound over the surface of the wood until it has fully dried. The result is a wood beam that deflects water and keeps the interior of the beam safe from moisture absorption, greatly enhancing the durability of the structure itself.
A similar process, known as a color wash, traded in the lime and tallow for natural compounds, animal compounds, and stale beer to accomplish the same end result. Both washes must be applied to wood beams on a regular basis in order for them to remain effective. Throughout history, annual or seasonal “washing” of wood was a common practice designed to ensure the long life of any wooden structure. Today, this is still performed on some structures for historical effect or to preserve their original nature.
Moving On: Oils and Stains Take Center Stage
Today, many wooden structures are preserved through a combination of oils and stains, some of which are actually native to the wood. Many softer woods actually come with a high amount of oil contained within the timber, which itself acts as a natural water deterrent and a great way for wood to self-preserve when used in construction. Harder woods, however, do not come with such built-in advantages. Furthermore, the naturally occurring oil within wood is not enough to defend against sustained moisture and extreme weather.
That’s where oil and stain application comes in. Modern day wood preservation originated with a substance known as creosote, created from distilling coal tar, was one of the first such oils to be applied to wood for the purpose of preservation. Though highly effective, the substance was eventually found to be toxic and is currently listed as a serious carcinogen.
Perhaps the lasting legacy associated with the era of oils and stains can be found in teak oil. This unique oil can help wooden beams repel water, but it can also be mixed with fungicides and other compounds that prevent the growth of molds and fungi. When put together, teak oil and fungicides can dramatically prolong the life of wood, and they’ve been doing so since about the 1950s. Many homeowners regularly apply teak oil to their existing structures, though some have moved on and have opted for varnishes instead.
Varnishes: Giving Wood Protection and Shine
Varnish has long been the preferred method of protecting wood, even when that wood is not being regularly exposed to the elements. Varnish simply involves melting down a natural resin and mixing it with linseed oil. The resulting substance is liquid and protective, drying on the surface of the wood and providing a shine that can’t be obtained with basic oils and stains. Because it essentially amounts to dried resin, varnish prohibits moisture from reaching the surface of the wood. Over time, this allows wood to completely resist the potential for mold, fungus, and rot.
Varnish does come with one fatal flaw, however: It simply does not protect against the penetration of UV rays. In the short term, that means varnish is likely to flake after a few years in use on a wooden beam. Eventually, homeowners will need to sand the beam down in order to remove all existing varnish and replace it with a fresh, flake-free coat. Though developments have recently been made in the creation of UV-resistant varnishes, many people simply opt for traditional compounds and commit to annual or seasonal refinishing.
Lead Paints: A Bygone Era in Wood Protection
Lead paint used to be just about everywhere, including on wooden beams outside the home where protection from the elements was needed. Lead actually provides a great way of protecting against moisture, especially combined with the drying properties of linseed oil. Some manufacturers even combined lead paints with varnishes, creating an enamel paint that lasted longer and offered an enhanced look to the wood after the paint had dried.
Of course, lead paint soon became outlawed by most governments around the world due to significant health concerns. Today’ a number of synthetic paints and compounds exist to perform the same task, including variants mixed with varnish and linseed oil. Without lead, however, their longevity is not quite the same.
Modern Options: An Alternative to Lead-Based Paint
In current usage, many homeowners have found oils, stains, and varnishes work quite well when protecting the wood used throughout their home’s exterior. Paints, though, are an area of primary concern. Some lead-based paints do still exist for exterior application, with lower-rated concentrations of lead that have been deemed safe by governments around the world. Most consumers bypass those options, however, for matte or glossy acrylic pants. These water-soluble pants release no toxic solvents or byproducts, but they do provide nearly the same level of protection as lead paints did nearly a half-century ago.
Many homeowners opt for traditional outdoor paints, largely without protective properties, and then top a layer of paint with a traditional varnish. This is a really great alternative to the lead-based paints of old, and it has the dual benefits of looking great and providing two distinct layers of protection against the elements.
No matter which option is chosen, consumers should make sure to follow a few simple guidelines when applying their stain, oil, varnish, or paint to an exterior wooden beam:
- Ensure that the wood is free of rot, fungus, mold or other decay. Sealing that decay in with paint will have disastrous long-term consequences.
- New wood should be properly seasoned.
- Wood should be properly cleaned and prepared for the application of a protective agent. This may involve consultation with the creator of the stain, oil, paint, or varnish used.
- After application, a regular schedule of inspection and revision should be undertaken so that the wood is never allowed to rot or decay in any substantial way.
With proper preparation and a policy of long-term vigilance, homeowners will find it relatively easy not only to protect the exposed wooden surfaces of their home’s exterior, but also to regularly revise the wood’s coating and ensure that it looks as good in ten years as it does on the day of installation.